1. Field of the Invention
The present invention relates to an electronic system that includes an electronic apparatus and a unit removably attached to the electronic apparatus.
2. Description of the Related Art
Generally, in an electronic apparatus such as a printer, components needing periodic replacement and devices for expanding or changing functions are required to be replaced on a per-unit basis. For example, in an electrophotographic printer, a fixing unit is one example of such a unit. Other examples of such units are an optional feeder and an optional paper discharge unit.
Imitations of such units have been appearing on the market with increasing frequency in recent years. If such an imitation product is attached to a printer, there is the danger that the printer will malfunction or that the printer body itself will be damaged. In particular, with regard to a unit such as a fixing unit requiring a very high reliability, urging the user to exercise caution is vital in the event that a genuine product has not been attached.
In accordance with the specification of Japanese Patent Application Laid-Open No. 2003-307982, an identification apparatus encrypts a random number and transmits the encrypted signal to an accessory. The accessory decrypts the encrypted random number, appends an ID to the decrypted random number, re-encrypts the random number and transmits the resultant random number to the identification apparatus. The identification apparatus decrypts the received random number and determines whether the decrypted random number matches the original random number. In this way it can be determined whether the accessory is a genuine product or not.
However, Japanese Patent Application Laid-Open No. 2003-307982 is indifferent with regard to data error and clock synchronization error. For example, data-shift error can occur with clock synchronization error as the cause (clock synchronization error is a phenomenon in which data is shifted in its entirety because one bit of data is missed). Data-shift error is undesirable because it brings about burst error. Data-shift error can arise especially in cases where a device on the receiving side is supplied with a clock externally.
In general, authentication failure occurs owing to mismatch of a key used in encryption. Even if key match is achieved, however, authentication will fail if data error occurs during communication. The reason for this is that the data before encryption and the data after decryption differ. As a result, despite the fact that a genuine unit has been attached, the decision rendered is that the unit is not genuine. This is undesirable from the standpoint of usability.
In accordance with the present invention, data-shift error and burst error that occur owing to clock synchronization error can be sensed in ideal fashion using a termination identifier. Accordingly, it is possible to distinguish between a genuine unit and a unit that is not genuine.